1. Field of the Disclosure
The present disclosure relates generally to optical communication networks and, more particularly, to inter-channel spectral shaping in optical ring networks.
2. Description of the Related Art
Telecommunications systems, cable television systems and data communication networks use optical networks to rapidly convey large amounts of information between remote points. In an optical network, information is conveyed in the form of optical signals through optical fibers. Optical networks may also include various network elements such as amplifiers, dispersion compensators, multiplexer/demultiplexer filters, wavelength selective switches, couplers, etc. configured to perform various operations within the network.
Optical networks may be configured using a ring topology, in order to provide dually redundant signal paths for improved reliability in the event of a network fault. The ring network may typically comprise a pair of optical fibers, with one fiber handling clockwise signal flow, and the second fiber handling counterclockwise signal flow. Typically, a ring network may carry multiple signal channels, using Wavelength Division Multiplexing (WDM) technology. Individual channels may be added to and dropped from the ring network by means of Wavelength Selective Switches (WSSs), for example. As used herein, a ‘channel’ refers to a logical connection over a multiplexed medium, and may be more narrowly defined as a continuous range of spectral frequencies that is distinct from other frequencies or ranges of frequencies, and which can be routed through the network at wavelength routing locations, independently of other channel entities.
WSSs may remove a channel from the ring by attenuating (i.e., blocking) the wavelengths associated with the removed channel, at the site where the channel is dropped. Blocking the wavelengths at the point after which they are no longer needed may allow the wavelengths to be reused in other sections of the ring. However, another aspect associated with attenuation of wavelengths by the WSS is net loop gain around a loop in a ring network. Specifically, when the net optical gain around a loop in an optical ring network becomes greater than unity (at any wavelength), the optical ring network may malfunction due to uncontrolled power buildup of circulating optical power. In many instances, propagation delays and nonlinear effects may cause the power buildup to appear chaotic, while the chaotic behavior is commonly referred to as ‘instability’. Accordingly, the blocking of wavelengths by a WSS may be a key factor in the operational stability of optical ring networks.